1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and, more particularly, to a method of forming a wiring layer on the surface of an interlevel insulator in a semiconductor device having a step portion on the surface of the interlevel insulator. In this case, the step portion is formed between a plurality of electrodes arranged under the interlevel insulator and/or between lower wiring layers or an interface between an element region and an element isolation region.
2. Description of the Related Art
In a semiconductor device, inclined portions, recess portions, and/or projecting portions are formed on the surface of an interlevel insulator by an electrode and a lower wiring layer. In these portions, a wiring layer having a width smaller than that of a wiring layer to be formed is formed. This is known as a problem so called "narrowing of wiring".
This narrowing of wiring occurs not only on an electrode and a lower wiring layer but near an interface portion between the element region and the element isolation region. In this case, a wiring layer having a width smaller than that of a wiring layer to be formed is formed.
When the wiring layer is to be formed on a surface of the interlevel insulator, an Al layer serving as a wiring layer is formed on the entire surface of the interlevel insulator. In this case, the Al layer has an uneven surface conforming with an uneven shape of the surface of the interlevel insulator. Thereafter, a resist is formed on the Al film, and the resist is exposed by a beam so as to be patterned. Sequentially, the Al layer is patterned using the patterned resist as a mask, thereby forming the wiring layer.
In the above process, when a positive resist (i.e., a type for removing an exposed portion) is used, a beam reflected by the inclined side of the uneven surface of the Al layer is received by the resist to narrow the resist. For this reason, the wiring layer is narrowed due to the narrowing of the resist.
When the wiring layer having the narrow portion is used, a wiring layer is easily discontinued upon forming of a surface protection film (not shown), thereby decreasing a yield of products. In addition, in this case, even when the wiring layer is not discontinued, the narrow portion of the wiring layer is easily degraded after the products are shipped, and the reliability of the wiring may be degraded, thereby degrading the device itself.
As described above, in the conventional semiconductor device, a wiring layer pattern is formed regardless of the presence of a step portion included in the underlaying film of a metal layer serving as a wiring layer. As a result, narrowing of wiring is caused, thereby decreasing a yield of products and degrading the reliability of the device.